synthetic corundum.7, flux, inclusions.5, gems

Five oval faceted synthetic blue flux sapphires, each weighing approximately 2 ct, grown by Chatham Industries were examined. The company had been experimenting with the growth of flux-melt blue sapphires for several years, but its early products were heavily included and unsuitable for faceting. The five recently examined stones were dark blue, with strong color zoning in two specimens. The zoning ranged from near colorless to deep blue and was confined to definite straight-sided, angular patches reflecting the growth and structure of the original crystal. Platinum flakes and splinters resembling submetallic included crystals were also observed. The most common inclusions were residual flux, which occurred as white, thick, veined, fingerprint-patterned curving layers, whitish curving and flowing smoke-like clouds, or a combination of both forms. The hydrostatic specific gravity ranged from 3.98 to 4.06, with platinum inclusions likely contributing to the higher values. Refractive indices were relatively consistent, ranging from 1.763 to 1.772, with a corresponding birefringence of 0.009. Spectroscopic examination revealed a very vague absorption band centered at 451.5 nm in the blue region, which was not diagnostic. X-ray fluorescence ranged from pale white through faint bluish white to yellowish white, with no phosphorescence observed after X-ray excitation. Under short-wave ultraviolet radiation, the sapphires showed dull brownish white fluorescence, while long-wave ultraviolet radiation produced a moderate whitish yellow glow. During exposure to both long- and short-wave ultraviolet radiation, two stones displayed distinct patches of bright yellow fluorescence. No inclusion centers for this fluorescence were observed under the microscope, and the bright yellow areas were not bordered by optically detectable irregularities.